Layered materials such as graphene have attracted considerable interest for potential applications in diverse electronic and optoelectronic devices, including transistors, inverters, photodetectors, photovoltaic devices, ultrafast lasers, polarizers, touch panels, and optical modulators. Unfortunately, the lack of a bandgap in graphene has constrained the on-off current ratio of graphene-based transistors for logic applications. Some attempts made to address this challenge have yielded improvements in the on-off ratio of resulting devices, but often at a severe sacrifice of a deliverable current density.
Also, with a broad spectral absorption, high carrier mobility, and short carrier lifetime, graphene exhibits exciting potential for wideband, high speed photodetection. However, the design of graphene-based photodetectors currently relies on a lateral graphene-metal junction with a rather small photoresponsive active area, which is not ideal for efficient photon harvesting. Additionally, the weak absorption characteristics and small built-in potential in these graphene-based photodetectors have severely limited their external quantum efficiency (EQE) in the range of about 0.1-1%.
It is against this background that a need arose to develop the vertically stacked heterostructures including graphene described herein.